The present invention relates to novel processes for producing 3-mercaptoalkane-1,4-diones.
Artificial flavoring agents for foodstuffs have received increasing attention in recent years. In many areas, such food flavoring agents are preferred over natural flavoring agents at least in part because of the uniform flavor that may be so obtained. For example, natural food flavoring agents such as extracts, essences, concentrates and the like are often subject to wide variation due to changes in the quality, type and treatment of the raw materials. Such variation can be reflected in the end product and results in unreliable flavor characteristics and uncertainty as to consumer acceptance and cost. Additionally, the presence of the natural product in the ultimate food may be undesirable because of increased tendency to spoil. This is particularly troublesome in convenience and snack food usage where such products as dips, soups, chips, prepared dinners, canned foods, sauces, gravies and the like are apt to be stored by the consumer for some time prior to use.
The fundamental problem in preparing artificial flavoring agents is that of achieving as nearly as possible a true flavor reproduction. This generally proves to be a difficult task since the mechanism for flavor development in many foods is not understood. This is notable in products having meaty and roasted flavor characteristics. It is also notable in products having vegetable-like and hydrolyzed vegetable protein-like and anise-like flavor characteristics
Reproduction of roasted and meat flavors and aromas and vegetable-like and hydrolyzed vegetable protein-like and anise-like flavors and aromas has been the subject of the long and continuing search by those engaged in the production of foodstuffs. The severe shortage of foods, especially protein foods, in many parts of the world has given rise to the need for utilizing non-meat sources of proteins and making such proteins as palatable and as meat-like as possible. Hence, materials which will closely simulate or exactly reproduce the flavor and aroma of roasted meat products and liver products and vegetable products are required.
Moreover, there are a great many meat containing or meat based foods presently distributed in a preserved form. Examples being condensed soups, dry-soup mixes, dry meat, freeze-dried or lyophilized meats, packaged gravies and the like. While these products contain meat or meat extracts, the fragrance, taste and other organoleptic factors are very often impaired by the processing operation and it is desirable to supplement or enhance the flavors of these preserved foods with versatile materials which have either roasted meat or gravy-like or vegetable-like or meat-like or ham-like nuances.
2-Alkylfuran-3-thiols and bis (alkyl-3-furyl) disulfides are disclosed in U.S. Pat. No. 3,723,475 issued on Mar. 27, 1973 to supply meaty flavor aroma and taste nuances to foodstuffs. 2-Thia-substituted-1,4-diones are disclosed in U.S. Pat. No. 3,836,563 issued on Sept. 17, 1974 to also supply meaty flavors to foodstuffs.
Swiss Pat. No. 531,313 discloses the addition of hydrogen sulfide across a double bond, eliminating the double bond.
Such a reaction, however, is not shown in conjunction with a chemical compound which has two ketone moieties.
The mechanism of the addition of hydrogen sulfide across a double bond of an alpha-beta-unsaturated ketone is set forth at lines 40-67 of columns 3 and 4 of Swiss Pat. No. 531,559. The formation of thio esters using thio acetic acid and unsaturated ketones is set forth at lines 15-20 of column 6 of Swiss Pat. No. 531,559.
U.S. Pat. No. 2,630,452 to Crouch, et al discloses processes for reacting unsaturated nitriles with thio acids whereby the thio ester moiety adds to the double bond at the "alpha" position with respect to the CN moiety using an aqueous alkali metal hydroxide catalyst or a quaternary ammonium compound catalyst. The substance of Crouch, et al may be illustrated by the following reaction between acrylonitrile and thioacetic acid: ##STR4## At column 2, lines 40-45, Crouch, et al states: "In accomplishing the thioacetic acid-acrylonitrile reaction, it has been found to be highly advantageous to employ certain basic catalysts as reaction promoters and directors. The preferred catalyst is a quaternary ammonium compound designated by the general formula . . . "
In example IV of Crouch, et al, acrylonitrile is reacted with thioacetic acid in the presence of a t-butyl hydroperoxide catalyst at a temperature of 43.degree.-49.degree. C.
U.S. Pat. No. 3,441,589 to Oswald discloses reaction of thiol compounds such as mercaptans and thiolcarboxylic acids being selectively added to esters which, in turn, are formed by the reaction of maleic acid, fumaric acid or maleic anhydride with terminally unsaturated alcohols such as allyl alcohol at either of the terminal double bonds of the ester functionality or at the maleic or fumaric side of unsaturation with the use of either free radical or ionic catalysts. At column 7, Example 8, Oswald teaches the reaction of diallyl maleate with thiolacetic acid to form n-(3-acetylthio)-propyl allyl maleate according to the following reaction: ##STR5## in the presence of a free radical catalyst, such as ultraviolet light or gamma radiation or a "wide variety of peroxidic and azo compounds" (see column 3, lines 60-62).
Reid "Organic Chemistry of Bivalent sulfur", Volume IV, 1962, Chemical Publishing Co., Inc.; discloses reactions of thioacetic acid with unsaturated compounds. At pages 15 and 16 Reid states:
"The most interesting reaction of thioacetic acid is its ready addition to unsaturates. An example of this is its addition to acrylonitrile. In this it exhibits its mercaptan character but in acitivity it far surpasses most mercaptans. Usually the addition takes place spontaneously and completely. With styrene the reaction is: ##STR6## The product is the beta-phenethyl ester of thioacetic acid and is identical with that from phenethyl mercaptan and acetyl chloride . . . " PA1 thioacetic acid PA1 thiopropionic acid PA1 thiobutyric acid PA1 thioisobutyric acid PA1 thio-n-pentenoic acid PA1 thiocinnamic acid PA1 thiobenzoic acid PA1 2-methyl-thiobenzoic acid PA1 3-methyl-thiobenzoic acid PA1 4-methyl-thiobenzoic acid PA1 2,4-dimethyl-thiobenzoic acid PA1 3,5-dimethyl-thiobenzoic acid PA1 Methyl thiazole alcohol (4-methyl-5-betahydroxyethyl thiazole); PA1 2-Methyl butanethiol; PA1 4-Mercapto-2-butanone; PA1 3-Mercapto-4-pentanone; PA1 1-Mercapto-2-propanone; PA1 Benzaldehyde; PA1 Furfural; PA1 Furfural alcohol; PA1 2-Mercapto propionic acid; PA1 2-Pentene; PA1 Alkyl pyrazine; PA1 Methyl pyrazine; PA1 2-Ethyl-3-methyl pyrazine; PA1 Tetramethyl pyrazine; PA1 Polysulfides; PA1 Dipropyl disulfides; PA1 Methyl benzyl disulfides; PA1 Alkyl thiophenes; PA1 2-Butyl thiophene; PA1 2,3-Dimethyl thiophene; PA1 5-Methyl furfural; PA1 Acetyl furan; PA1 2,4-Decadienal; PA1 Guiacol; PA1 Phenyl acetaldehyde; PA1 .delta.-Decalactone; PA1 d-Limonene; PA1 Acetoin; PA1 Amyl acetate; PA1 Maltol; PA1 Ethyl butyrate; PA1 Levulinic acid; PA1 Piperonal; PA1 Ethyl acetate; PA1 n-Octanal; PA1 n-Pentanal; PA1 Hexanal; PA1 Diacetyl; PA1 Monosodium glutamate; PA1 Sulfur-containing amino acids; PA1 Cysteine; PA1 Hydrolyzed vegetable protein; PA1 Hydrolyzed fish protein; and PA1 Tetramethyl pyrazine
Hydrolysis of a thio ester to a thiol is set forth at page 446 of chapter 36 of "Organic Sulfur Compounds " Volume 1, Editor: N. Kharash, Pergamon Press 1961 London.
No teaching exists in the prior art to show that, given the structure: ##STR7## where R.sub.2 is lower alkyl and R.sub.1 is hydrogen, the effect of carrying out a reaction of a 2-ene-4-one-1-al with a thioacid (in the presence of base) is directive leading substantially to a reaction product where the thioester substitution is alpha to the ketone moiety and not the aldehyde moiety.
Furthermore, given the 2-ene-1,4-dione reactants of our invention, there is no prediction in the prior art that either (i) no catalyst is necessary in the case of using a hex-3-ene-2,5-dione reactant, or (ii) a basic catalyst is needed and the addition is directive in the case of using a pent-2-ene-4-one-1-al.